Research On Ion Beam Figuring System And Processing Technology For Large Aperture Optics

With the development of modern science and technology,large aperture optical systems are widely used in high-tech fields such as space science research,astronomy optics,ground-based space target detection and recognition.At present,the development of large aperture optical systems presents two prominent features.One is the diameter of optical components is becoming larger and larger,and the other is the accuracy of surface error is getting higher and higher.This puts higher requirements on the processing of optical components and promotes the development of optical processing technology.The processing of large aperture optical components includes many stages such as lens body forming,milling,grinding and polishing,and polishing is the most important follow-up process.The traditional polishing methods have the disadvantages of long processing time and slow convergence,and it is difficult to meet the processing requirements of optical components.Therefore,many advanced deterministic polishing techniques such as small grinding heads,stressed lap,magnetorheological finishing(MRF),bonnet polishing,and ion beam figuring(IBF)have appeared.Among these methods,IBF has the highest processing accuracy,and is usually used as the last polishing process,so its polishing accuracy determines the highest precision that the optical components can be polished.In the late 1980s,a large-scale IBF system has been successfully developed and applied to the processing of astronomical telescopes in America.In this century,France,Germany,and Italy have also developed large-scale IBF systems.Given the huge commercial and military value of large-scale IBF systems,we must carry out relevant research work.This article has carried out the research work of the large-scale IBF system on the existing basis of the research group,the relevant content mainly includes the following parts:1.A large IBF system named KDIBF2000 has been developed.Extensive design optimization work have been done.Double vacuum chambers and duplex processing systems improve the processing efficiency and utilization of the machine.Five-axis motion system realizes high-precision control of ion source,and makes the ion beam can process a variety of complex surface parts.Multi-objective optimization design of the key components of the machine improves the dynamic and static performance of the machine.The dynamic and static performance testing and sample processing all confirms the machine has an excellent processing performance.The development of the machine laid the foundation for the IBF of large aperture workpieces.2.Fast convergence processing technology of large aperture optical components is researched.The dwell time algorithm is a key issue in the polishing of large aperture workpieces.In order to improve the surface error convergence efficiency,we proposes a filter iteration method based on pulse iteration method and a dual beam diameter combination process method based on linear equation.The analysis shows that both they can save processing time without reducing the machining accuracy,thereby improving the processing efficiency.Since IBF is the last processing step of the workpiece,the accuracy of removal function is directly related to whether the rapid convergence process can achieve high efficiency and high precision processing.Based on the above objectives,the effect of removal function error on processing accuracy is analyzed.And we propose an error identification and compensation method of removal function.3.Ion beam figuring method to correct the edge effect is researched.Edge effect is regarded as one of the most difficult technical issues for fabricating large primary mirrors.IBF has the advantage of no edge effect and is an ideal method for correcting the edge effect.First,the theoretical model and process flow for ion beam correction edge effect were established.Secondly,the problems of the edge correction of ion beam correction are analyzed.Secondly,the problems of ion beam correction edge effect are analyzed.One is that the edge can't be completely removed,and the other is the phenomenon of over removal at the middle intersection.The two major problems are solved by the method of edge data extension and external starting figuring point.Finally,the feasibility of the ion beam correction edge effect was verified through a process test.4.Based on the above research,a number of large aperture optical components were polished by IBF,including large aperture rectangular mirrors and a high-precision Zerdour plane mirror,and surface error can be quickly converged to meet the processing accuracy requirements.The test results verify the capability of the polishing system and the correctness of processing technology for large aperture optics.